Variation in Bird Songs

A study of bird songs soon shows that while the songs of different birds of a given species are much alike in the rhythm, there is a great variation in different individuals in the notes used and in the excellence of rendering, so that the ear trained to bird music soon distinguishes different robins and different orioles through their songs.

There may also be a variation in the song of any one individual, dependent on age and season. The first efforts of the young bird to sing are not so near the type of that species as those which he makes in later seasons. Again the song of the individual may change as the season progresses, the song becoming shorter and shorter till it ceases altogether.

Mr. Oldys reports that he has noted more than eighty different wood thrush phrases, and he says that song sparrows' phrases are more diverse than those of wood thrushes. A song sparrow has been known to render twelve distinct themes in fifteen minutes.

Individual differences are due, not only to the use of different phrases, but also to the way in which the phrases are rendered. There may be excellent rendering and poor rendering of the same phrase among birds, just as there are varying degrees of excellence among human voices.

Range of voice. A study of the records made of bird songs suggests the pitch and range for different birds. The tones of nearly all birds are high-pitched, ranging between two and four octaves above middle C. The range of voice in different species varies from three notes for the chickadee to two octaves for the hermit thrush. A number of birds have a range of about one octave.

Call notes. Besides their songs, birds also make sounds known as "call notes," which differ from their songs in about the same way that human lan­guage differs from human songs. These call notes probably serve the purpose of a language by which birds communicate. They are used by all birds, both male and female, and at all times of the year.

Some birds have a great variety of call notes, each representing some emotion, such as a hunger call, given by the young birds in the nest; the lost call of a young bird after leaving the nest; the warning call given to the young to show no signs of life in the face of danger; the recognition call, by which individuals of the same species are brought together in flocks, especially during migration; and the rally cry by which other birds are brought to the spot. An ob­server of the crow has recorded twenty-seven dis­tinct calls for this bird.

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